Spot light is not working in preview render
If the sun is working (the hemi light isn't supported in Cycles – it basically just acts like a sun) the problem is most likely due to light falloff of your light sources. your scene is too large for the size and strength of your lamp.

You can confirm that by adding a light falloff node to the emission of your light as shown below.


quadradic is the default (and real world) falloff
linear is a linear falloff (double the distance, half the strength of the light)
constant is no falloff, this is i.e. used per default by the sun lamp




Adjust the falloff and strength to fit your needs.